Reference local PHPUnit schema (#343)

Author: ben-challis

phpunit.xml.dist

@@ -2,7 +2,7 @@
 <phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          colors="true"
          bootstrap="vendor/autoload.php"
-         xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.3/phpunit.xsd">
+         xsi:noNamespaceSchemaLocation="vendor/phpunit/phpunit/phpunit.xsd">
     <coverage>
         <include>
             <directory>./src/</directory>